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function FileLastModified(const sFile: TFilename): TDateTime;
var sr: TSearchRec;
    tzi: TTimeZoneInformation;
    lt, st: TSystemTime;
begin
  if FindFirst(sFile, faAnyFile, sr) = 0 then
    begin
      GetTimeZoneInformation(tzi);
      FileTimeToSystemTime(sr.FindData.ftLastWriteTime, st);
      SystemTimeToTzSpecificLocalTime(@tzi, st, lt);
      Result := SystemTimeToDateTime(lt);
      SysUtils.FindClose(sr);
    end
  else
    Result := 0;
end;					

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function MyGetFileTime(FileName: PChar): TDateTime;
var
  FileHandle: Cardinal;
  LastWriteTime: TFileTime;
  UTCSystemTime, LocalSystemTime: TSystemTime;
begin
  Result := 0;
  FileHandle := CreateFile(PChar(FileName), GENERIC_READ, FILE_SHARE_READ,
    nil, OPEN_EXISTING, 0, 0);
  if FileHandle = INVALID_HANDLE_VALUE then
    Exit;
  if not GetFileTime(FileHandle, nil, nil, @LastWriteTime) then
    Exit;
  FileTimeToSystemTime(LastWriteTime, UTCSystemTime);
  SystemTimeToTzSpecificLocalTime(nil, UTCSystemTime, LocalSystemTime);
  Result := SystemTimeToDateTime(LocalSystemTime);
  CloseHandle(FileHandle);
end;					

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var
  WriteTime: TDateTime;
begin
  if OpenDialogX.Execute then
  begin
    WriteTime := MyGetFileTime(PChar(OpenDialogX.FileName));
    if WriteTime <> 0 then
      ShowMessage(DateTimeToStr(WriteTime))
    else
      ShowMessage('Fehler');
  end;